As a method of forming a thin film on a semiconductor wafer (hereinafter referred to as a “wafer”) as a substrate, a plasma enhanced atomic (molecular) layer deposition (PE-ALD (MLD)) (hereinafter, ALD and MLD are collectively referred to as “ALD”) is known. In such a PE-ALD, a wafer is exposed to a source gas containing a precursor of a thin film such that the source gas containing a constituent element of the thin film is adsorbed onto the wafer. Then, the wafer onto which the source gas is adsorbed is exposed to plasma of a reaction gas. The reaction gas decomposes the aforementioned precursor or supplies other constituent elements capable of being coupled to the constituent element of the precursor, thereby to form a desired atom layer or molecular layer on the wafer. In the PE-ALD, a thin film in which the atom layers or the molecular layers are deposited by repeating the above processes is formed on the wafer.
As an apparatus for performing the PE-ALD, a sheet-wafer type film formation apparatus and a semi-batch type film formation apparatus are known. In the sheet-wafer type film formation apparatus, wafers are loaded into a vacuum container one by one, and a source gas and a reaction gas are alternately supplied into the vacuum container. In the semi-batch type film formation apparatus, an inner space of a vacuum container is partitioned into a region to which a source gas is supplied and a region to which a reaction gas is supplied, and wafers sequentially pass through these regions. The semi-batch type film formation apparatus supplies the source gas and the reaction gas in different regions, thus simultaneously processing a plurality of wafers. Thus, the semi-batch type film formation apparatus is advantageous in that it has higher throughput than the sheet-wafer type film formation apparatus.
For example, the present inventors developed a first semi-batch type film formation apparatus, in which a rotatable table (mounting stand) that is rotatable around an axis thereof is installed inside a vacuum container (this is expressed as a “process container” in the related art and this expression is similarly applied even in the Background section of the present disclosure), and the interior of the vacuum container is partitioned into a first region to which a source gas (precursor gas) is supplied and a second region to which a plasmarized reaction gas is supplied. A plurality of wafers is arranged on the rotatable table in a circumferential direction. With the rotation of the rotatable table, each of the wafers repeatedly passes through the first and second regions in an alternate manner so that a film formation process is performed on each of the wafers.
In such a first film formation apparatus, the first region is configured as a fan-shaped space defined by partitioning a portion of a circular space above the rotatable table in the circumferential direction, and the second region is defined by the remaining space. The first region is separated from the second region by an exhaust port formed to surround discharge portions (injection portions) from which the source gas is supplied, and a separation gas supply port (injection port) formed to surround the exhaust port and supply a separation gas (purge gas) therethrough.
According to this film formation apparatus, the second region to which the reaction gas is supplied and requires a longer reaction time than a time required in adsorbing the source gas, is increased in size, thus forming a thin film having good film quality.
On the other hand, there may be a case where the thin film thus formed includes a portion in which coupling between atoms constituting the thin film is not sufficiently achieved. As such, for example, after a film formation process is completed, there is a need to stop the supply of the source gas and perform a post-process which includes switching a gas to be plasmarized to a post-process gas such as hydrogen, and coupling dangling bonds of atoms in the thin film to densify the thin film.
However, if the post-process that switches the gas to be supplied into the vacuum container is additionally performed after the film formation process, a period of time from when a wafer is carried into a film formation apparatus till when the wafer is carried out of the film formation apparatus is prolonged, which causes deterioration in process efficiency of the film formation apparatus.
Moreover, there is a case where a reaction gas immediately after adsorbed onto the wafer contains impurities derived from a precursor. At this time, a pre-process of removing the impurities with a pre-process gas containing a plasmarized hydrogen or the like is performed before causing a source material adsorbed onto a substrate to react with the reaction gas, which makes it possible to improve a film quality of a thin film. However, in the first film formation apparatus according to the related art, since the regions (the first region and the second region) inside the vacuum container are filled with the source gas or the reaction gas, it is difficult to perform such an impurity removal process during a time period from when the source gas is adsorbed onto the substrate till when the source gas reacts with the reaction gas.
In addition, there is known a second semi-batch type film formation apparatus in which an activation gas injector is installed in a direction crossing a movement direction of wafers that are circumferentially arranged on a rotatable table. However, the second film formation apparatus has a structure in which a portion of a ceiling surface constituting a vacuum container is formed to approach the rotatable table so as to form a restricted space. This structure separates regions (process regions) to which different gases are supplied. Accordingly, the second film formation apparatus is different in type from the first film formation apparatus.
Thus, the second film formation apparatus does not describe the configuration in which the aforementioned pre-process or post-process can be performed inside a film formation apparatus in which the interior of a vacuum container to which a reaction gas is supplied is not partitioned into a plurality of spaces as in the second region of the first film formation apparatus.